In the 3rd Generation Partnership Project's (3GPP's) release 10 of the Long-Term Evolution-Advanced (LTE-A) standard (hereinafter “LTE-A Rel. 10”), downlink spatial multiplexing transmissions may be multiple-input, multiple-output (MIMO) communications done in either a closed-loop operation mode, for low mobility scenarios, or an open-loop operation mode, for high mobility scenarios.
In LTE-A Rel. 10, a user equipment (UE) may be configured with up to four antennas with support for up to four layers of spatial multiplexing in single-user (SU) MIMO uplink communications. However, uplink spatial multiplexing MIMO communications may only be done in the closed-loop operation mode.